(1) Field of the Invention
The present invention relates to landing gear provided with energy absorber means, to an aircraft provided with said landing gear, and to a method of landing.
(2) Description of Related Art
Conventionally, an aircraft includes landing gear via which it stands on a contact surface. It should be observed that in the text below, the term “contact surface” is used to mean the contact surface against which the contact means bear on landing. For example, the contact surface may include ground as such, the deck of the ship, the roof of a building, or indeed a liquid surface such as water in particular when alighting at sea.
For example, the landing gear may be provided with three or four wheeled undercarriages that constitute a polygon for supporting the aircraft. Landing gear is also known that is provided with skids.
Such landing gear may be retractable in order to improve the aerodynamic drag of the aircraft. The most prominent elements of the aircraft are folded into the fuselage, and in particular retractable undercarriages of the landing gear. More precisely, each undercarriage is retracted in flight into a compartment conventionally referred to as a “wheel well”, ready to be deployed at the required moment prior to landing.
Civil certification regulations, e.g. known under the acronyms “FAR”, “JAR”, or “EASA-CS” (for European aviation safety agency certification specification) require undercarriages to absorb certain levels of kinetic energy.
Thus, according to such civil certification regulations, an undercarriage must be capable of absorbing the kinetic energy of an aircraft at a first predetermined vertical speed of impact against the contact surface without that leading to permanent deformation of the components making up the undercarriage, and with this applying for various attitudes of the aircraft on touchdown and for the most unfavorable conditions of weight and centering. It should be observed that plastic deformation of certain elements of a skid undercarriage may be acceptable.
Likewise, each undercarriage must be capable of absorbing the kinetic energy of an aircraft at a second predetermined vertical speed of impact against the contact surface, which second speed is greater than said first speed, and without breaking the components that constitute the undercarriage, for various attitudes of the aircraft on touchdown and for the most unfavorable conditions of weight and centering.
Landing gear complying with civil certification requirements is referred to for convenience as a “standard” landing gear.
Such standard landing gear is most effective and serves to satisfy the requirements of civil certification regulations. Nevertheless, it can be understood that standard landing gear is sometimes not suited to vertical speeds of impact against the contact surface that are faster than the speed defined by the civil regulation. Similarly, it can readily be understood that standard landing gear is ineffective on water since it penetrates into the water without absorbing significant energy.
Unfortunately, in the event of a crash, the aircraft may be confronted with vertical speeds that are faster than the speeds set down by civil certification regulations. The landing gear can then be damaged, since the landing gear is then subjected to forces for which, by definition, it was not initially designed. Similarly, those forces greater than the usual forces are applied to the structure of the aircraft via the fastening points of the landing gear and, as a result, can give rise to dangerous damage.
In addition to civil certification regulations, there also exist military qualification regulations, e.g. known under the name “MIL-S-8698” or naval qualification regulations, e.g. known under the name “AR56” that are more severe than civil certification regulations. These military qualification regulations set down vertical speeds that are faster than the above-mentioned first and second vertical speeds.
Under such circumstances, standard landing gear does not necessarily comply with military qualification regulations.
Furthermore, it should be observed that standard landing gear does not absorb energy when ditching on water.
Document WO 2008/054401 presents additional energy absorber means.
Those energy absorber means comprise an inflatable cushion, usually known as an “airbag”, that is arranged under the bottom portion of a helicopter fuselage.
Furthermore, the energy absorber means are provided with a first source of gas for inflating the airbag, a second source of gas for reinflating the airbag, and an air vent that may be in an open position or in a closed position.
The system described is advantageous insofar as it provides the aircraft with additional capacity to absorb energy. Nevertheless, it will be understood that the bottom portion of the fuselage needs to be reinforced in order to withstand the forces that result from landing, since the fuselage is not normally dimensioned for that purpose.
Furthermore, the bottom portion must not possess elements that might damage the airbag, such as antennas, for example.
As a result it would appear to be difficult to implement that solution on an existing aircraft without giving rise to constraints, or at least to difficulties, and in any event to modifications and to reinforcements.
Also known are the following documents: DE 202 09 258 U1, U.S. Pat. No. 2,621,874 A, EP 0 869 058 A2, and WO 92/00876 A1.